serendipity

ser-en-dip-i-ty/ˌsɛɹənˈdɪpɪti/US

noun

1
The phenomenon of making an unplanned, fortunate discovery through a combination of unexpected circumstances and insightful recognition.
2
An unsought, unintended or unexpected, but fortunate, discovery or learning experience that occurs by accident.
3
The occurrence and development of events by chance in a happy or beneficial way.

Coined in 1754 by Horace Walpole from the Persian fairy tale "The Three Princes of Serendip", whose heroes kept making lucky discoveries.

Also useful for “serendipity”:Crossword— A long fill for tough grids